The present invention relates generally to semiconductor device manufacturing and, more particularly, to barrier layer formation for metal interconnects through enhanced impurity diffusion.
Integrated circuits are typically fabricated with multiple levels of patterned metallization lines, which are electrically separated from one another by interlayer dielectrics containing vias at selected locations, to provide electrical connections between levels of the patterned metallization lines. In recent years, copper (Cu) has replaced aluminum (Al) as the metal of choice for wiring of microelectronic devices, such as microprocessors and memories. However, copper has a tendency to diffuse through insulators, such as silicon dioxide, during high temperature processes. As a result, the use of copper wiring also necessitates the placement of efficient diffusion barriers surrounding the copper wires, thereby keeping the copper atoms confined to the intended wiring locations and preventing circuit malfunctions, such as shorts.
As these integrated circuits are scaled to smaller dimensions in a continual effort to provide increased density and performance (e.g., by increasing device speed and providing greater circuit functionality within a given area chip), the interconnect linewidth dimension becomes increasingly narrow, which in turn renders them more susceptible to other deleterious effects such as electromigration. Electromigration is a term referring to the phenomenon of mass transport of metallic atoms (such as copper) which make up the interconnect material, as a result of unidirectional or DC electrical current conduction therethrough. More specifically, the electron current collides with the diffusing copper atoms, thereby pushing them in the direction of current travel. Over an extended period of time, the accumulation of copper at the anode end of the interconnect material significantly increases the local mechanical stress in the system. Most of this unwanted motion takes place along the surface of the copper, and in turn may lead to delamination, cracking, and even metal extrusion from the copper wire, thereby causing an electrical short to adjacent interconnects.